In the “What’s Cookin’” episode of Tales From the Crypt, the cook served Meat Loaf.
Note the capital letters.
Basil: I fought in the Korean War, you know. I killed four men.
Sybil: He was in the Catering Corps. He used to poison them.
Shakespeare homage.
Titus Andronicus bakes the two sons of Tamora and feeds the pie to their mother.
In Criminal Minds episode “Lucky,” a cannibalistic serial killer runs a restaurant and feeds one of his victims to the search party looking for his last victim, in the form of chili.
In The Mentalist episode “Red Herring,” a sous chef kills her boss during a cooking competition by spiking her pepper with ricin.
Was the killer in last year’s, Adult Swim’s “Too Many Cooks” that exploded the internet actually a cook? I know he ate some people bits. I’d look it up and watch it again, but then I’d be singing that damn song for the next week. Actually, it might be too late to avoid that, even without looking it up.
What if the onion was a terrorist organization?
Many layers, you see.
Just for fun, real life: http://www.ntnews.com.au/news/northern-territory/a-fannie-bay-pizza-cook-threatens-co-worker-with-scary-topping/story-fnk0b1zt-1227527844606
Nah, she’s all “Oh, phooey, I burned the darn muffins.”
If she walks into a bar, though…
Another Stout chef-murderer can be found in the short “Fourth of July Picnic.”
Excelllent performance from the late Chris Penn (brother of Shaun).
Clint Eastwoods character in the Eiger Sanction
John Waters film Desperate Living a queen is cooked and consumed by her subjects.
in Mongol, Genghis Khan’s father, a lesser Khan, was offered some food by some nameless tribesmen and obliged by custom to eat it. They were assassins and he died.
Bruce Glover and Putter Smith were hit men posing as waiter/sommeliers in Diamonds Are Forever.
Danny Aiello in Léon: The Professional was a restauranteur and a banker for criminals. He also tried to kill Natalie Portman, so he counts.
Clemenza in The Godfather. Cooked up a mean spaghetti. The secret was sugar and wine, iirc.
Garlic sliced so thin that it would disolve in the sauce. 
[Ray Liotta as Henry Hill] He used a razor blade to cut it so thin that it practically liquefied in the pan.[/RLaHH]
Chris Penn is dead? (checks wikipedia). Wow, nearly 10 years.
And his brother’s name is spelled “Sean”, and pronounced “Sin” (at least according to the Church lady).
Bob Hoskins in Felicia’s Journey - it was fairly heavily implied that he had killed a bunch of young women in the past.
Murder Under Glass, Columbo - restaurant critic and amateur chef Louis Jourdan
bumps off a restauranteur who’s threatening to expose Jourdan’s blackmailing. His preparation of fugu requires some serious cooking chops, as does his use of the fish’s toxin.
Now that I think of it, it was the NY hotel owner (Liggett?), not one of the chefs, who was the murderer.
Bender’s cooking in Futurama was bad enough to cause his mentors stomach to explode, I guess that would count.